1. Field of the Invention
The present invention relates to an on-vehicle display unit having a projecting sub-unit that projects an image, which is displayed on a display disposed in a dashboard of a vehicle, on a windscreen or an auxiliary screen. The image is superimposed over the fore ground which can be seen through the windscreen or the auxiliary screen.
2. Related Art
Recently, with increase of information for operation of a vehicle, an auxiliary display unit, which is called as a head-up display, is used to allow a driver to see additional information necessary for the vehicle operation which is over the capacity of indicators of the vehicle. The additional information is superimposed over the foreground visible through a wind screen of the vehicle without a larger change of a sight line of the driver.
In such on-vehicle display units, it is desired that sight distances do not vary too much when the driver frequently changes his sight between the superimposed information and the foreground. Therefore, a larger optical distance from a display of the information to the windscreen is preferably provided so that a sight point of a superimposed virtual image is nearer to the foreground.
However, the elongated sight distance of the virtual image is disadvantageous when the vehicle is stopping. That is because the driver will desire to clearly see the superimposed information.
As described above, such types of on-vehicle display units preferably make a focused point of a superimposed virtual image nearer to the foreground during an operation state of the vehicle, while the focused point is preferably positioned nearer to an eye position of a driver during a stopping state of the vehicle. To achieve both the focused points, a display may be moved to change an optical path distance from the display to a screen. However, the movement of display is undesirable, because it requires an enlarged space for receiving the display.
Such a display is generally accommodated in a dashboard. The display may be mounted on a ceiling of the vehicle, but the arrangement of the display near the head of a driver may make the driver feel pressure.
However, it is not practical that the dashboard is expanded forward, because the dashboard is forwardly adjacent to an engine room of the vehicle. Furthermore, it is undesirable for the driver that the virtual image on the windscreen is moved in a lateral direction of the vehicle.
Therefore, the dashboard can be expanded only backward to accommodate the display of the display unit in the dashboard.
However, the dashboard is provided with instruments such as a speed meter and a tachometer at a rear side thereof. If the instruments are disposed nearer to the driver due to the backward expansion of the dashboard, the driver needs a much change of a sight distance to change his sight between the instruments and the foreground.
In view of the aforementioned situations, a first object of the invention is to provide an on-vehicle display unit which can project an image displayed on a display in a dashboard toward a windscreen disposed outside the dashboard, thereby superimposing the image over the foreground visible through the windscreen. The on-vehicle display unit can move the superimposed image nearer to the foreground and away from the foreground in accordance with a kind of information included in the image. This configuration requires little enlargement of the accommodation space of the dashboard.
For achieving the first object of the invention, a first aspect of the invention is an on-vehicle display unit for projecting an image on a screen, the image displayed on a display in a dashboard of a vehicle, the screen disposed outside the dashboard, the screen being transparent so that the foreground is visible through the screen with the image projected on the screen being superimposed over the foreground. The on-vehicle display unit includes:
a reflecting mirror disposed in the dashboard for reflecting light emitted from the image displayed on the display toward the screen,
a semi-transparent mirror disposed in the dashboard between the display and the reflecting mirror, the semi-transparent mirror being able to pass partially and to reflect partially light emitted from the image on the display, and
an angle changing mechanism for selectively changing the semi-transparent mirror relative to a longitudinal direction of the vehicle into a first inclination angle position or a second inclination angle position,
wherein the semi-transparent mirror partially reflects the light of the image displayed on the display toward the screen when the semi-transparent mirror is at the first angle position, and the semi-transparent mirror partially reflects light reflected by the reflecting mirror toward the screen when the semi-transparent mirror is at the second angle position.
Thus, the semi-transparent mirror is selectively changed into the first inclination angle position or into the second inclination angle position. At the first angle position, light emitted from the image displayed on the display is reflected by the semi-transparent mirror toward the screen, thereby providing a shorter optical path from the display to the screen. Meanwhile, at the second angle position, light emitted from the image displayed on the display passes through the semi-transparent mirror to reach the reflecting mirror so that the light is reflected by the reflecting mirror to come again to the semi-transparent mirror which reflects the light toward the screen, thereby providing a longer optical path from the display to the screen. This allows the changeable position of the image from an eye of the driver with no movement of the display.
Preferably, the angle changing mechanism has a shaft extended in a lateral direction of the vehicle for turning the semi-transparent mirror around the shaft to selectively change the semi-transparent mirror into the first angle position or into the second angle position.
Thus, the semi-transparent mirror is easily changed to the first position or to second position by turning the semi-transparent mirror around the shaft.
Preferably, the on-vehicle display unit further has an image magnifying optical element disposed in the dashboard such that light from the reflecting mirror to the semi-transparent mirror passes through the image magnifying optical element for magnifying the image.
Thus, a virtual image with an appropriate size is visible by way of the screen at the second position of the semi-transparent mirror, although an optical path from the display to the screen is elongated by the provision of the reflecting mirror to make the sight distance of the image nearer to the foreground.
Preferably, the image magnifying optical element is a Fresnel lens having a flat surface at one side thereof and a Fresnel surface at the other side thereof, the flat surface facing the reflecting mirror in an optical direction of the image emitted from the display.
Thus, the Fresnel lens is positioned between the semi-transparent mirror and the reflecting mirror so as not to prevent change over of the semi-transparent mirror between the first and second positions. Thereby, the display unit is capable of the magnification of the superimposed image and is capable of the selection of the sight distances of the image.
A second object of the invention is to provide an on-vehicle display unit which can project an image displayed on a display in a dashboard toward a windscreen disposed outside the dashboard, thereby superimposing the image over the foreground visible through the windscreen. The on-vehicle display unit can position the superimposed image nearer to the foreground even when a projecting sub-unit is disposed in the dashboard. In the on-vehicle display unit, a driver can also see indications of measuring instruments such as a speed meter.
For achieving the second object of the invention, a second aspect of the invention is an on-vehicle display unit having a projecting sub-unit disposed in the dashboard for projecting an image on a first screen disposed above the dashboard, the image displayed on a first display in a dashboard of a vehicle, the first screen being transparent so that the foreground is visible from an eye position of a driver through the first screen with the image projected on the screen being superimposed over the foreground, the on-vehicle display unit includes:
a second screen disposed nearer to the eye position than the projecting sub-unit for projection of data obtained by measuring instruments of the vehicle, the second screen being visible directly from the eye position and
a second display disposed nearer to the eye position than the dashboard for indicating the data of the measuring instruments,
wherein a virtual image of the data obtained by the measuring instruments is visible from the eye position by way of the second screen.
Thus, in the on-vehicle display unit, the driver can see both the data obtained by the measuring instruments and the foreground with a less difference of sight distances thereof. Because, the second screen is disposed to project the data of measuring instruments of the vehicle.
Preferably, the projecting sub-unit has a reflecting mirror for reflecting light emitted from the image displayed on the first display toward the first screen.
Thus, the projecting sub-unit can elongate an optical path from the first display to the screen.
Preferably, the projecting sub-unit has a second reflecting element spaced from the first display in a longitudinal direction of the vehicle, and the reflecting mirror is a semi-transparent mirror which can pass partially light emitted from the first display toward the second reflecting element, the second reflecting element reflecting the light toward the semi-transparent mirror such that the light is reflected toward the first screen by the semi-transparent mirror.
Thus, the light emitted from the image displayed on the first display passes through the semi-transparent mirror to reach the second reflecting element so that the light is reflected by the second reflecting element to come again to the semi-transparent mirror which reflects the light toward the screen, thereby providing a longer optical path from the first display to the first screen.
Preferably, the second screen is another reflecting mirror, and the on-vehicle display unit has a combined plate extended substantially perpendicular to an optical axis of light emitted from the image displayed on the display, the combined plate having a first surface facing the display and a second surface facing the eye position, the second reflecting element defined in the first surface, the second screen defined in the second surface.
Thus, the second reflecting element and the reflecting mirror of the second screen are defined by the combined plate to be better for simplification of the display unit.
Preferably, the reflecting mirror of the projecting sub-unit is movable in an optical axis direction of the light emitted from the image displayed on the first display.
Thus, the on-vehicle display unit allows the driver to see both the data of the measuring instruments and the foreground with a less difference of sight distances thereof. Because, the reflecting mirror is movable in an optical axis direction of the light emitted from the image displayed on the first display.